Detector apparatuses of the kind recited above often have a temperature-dependent dark current that causes noise. This dark current can be decreased by cooling.
DE 10 2009 036 066 A1 describes an optoelectronic detector that comprises a cooling apparatus, specifically a Peltier element, connected thermally conductively to the detector. To avoid the occurrence of condensation on a surface of the optoelectronic detector, a sensor is provided for ascertaining an instantaneous value with regard to the ambient relative humidity and the ambient dew point temperature. The sensor is connected to a control unit that controls the cooling apparatus as a function of the value. This optoelectronic detector has the advantage that cooling is not entirely dispensed with. It has the disadvantage, however, that the actual cooling output is limited to a small magnitude, namely to the magnitude at which no condensation occurs. The ultimate result of this is that detector noise is only insufficiently eliminated.
The same document mentions another detector apparatus in which the detector plus the cooling apparatus, typically a Peltier element, are encapsulated in an airtight housing that is filled with a dry gas or is evacuated. With this apparatus, the waste heat of the cooling apparatus can be delivered to a cooling element that is connected thermally conductively to the cooling apparatus, and/or can be used to heat other components, for example an entry window of the housing. This detector apparatus is, however, identified as disadvantageous because the airtight encapsulation is complex.
It has in fact been found in practice that this detector apparatus has even further disadvantages. In particular, cooling is often not very effective. In addition, cooling proves to be particularly difficult when the detector must be at a different electrical potential level than the housing. In this case the Peltier element cannot simply be arranged between the housing and detector. A potential difference of this kind is usually necessary when acceleration of photoelectrons is intended to occur inside the detector.
Detector apparatuses in which an active cooling apparatus is respectively provided on a side facing away from a light incidence side of a light sensor are described, for example, from U.S. Pat. No. 5,508,740, U.S. Pat. No. 5,596,228, or U.S. Pat. No. 4,833,889. These detector apparatuses have the disadvantage that much of the cooling output is unused and lost.